1. Field of the Invention
The present invention relates to the manufacture of semiconductor devices. More particularly, the present invention relates to the integration of radio frequency (RF) features, RF devices, microwave features, and microwave devices into standard complementary metal oxide semiconductor (CMOS) chips.
2. Description of the Related Art
Today""s semiconductor devices are continually being pushed to meet stricter demands. As devices using this technology inundate the marketplace, consumers place higher demands on the devices. These demands includes smaller, more compact devices with greater functionality.
In order to meet the demands, semiconductor devices employ CMOS chips and RF chips. Such devices include, for example, cellular phones that require both digital CMOS circuitry as well as RF circuitry to enable wireless communication. Conventionally, in order to integrate both digital CMOS and RF circuitry onto one chip, manufacturers have been forced to use co-axial interconnect lines to handle the RF signals.
However, current high speed technology using CMOS circuitry suffers large losses of power. Today""s devices are expected to handle high speed applications such as RF and microwave applications. In the near future, standard digital CMOS interconnects will be expected to run at frequencies up to and greater than 1 GHz.
In addition, the use of a co-axial interconnect line presents other problems. FIGS. 1A and 1B represent a cross-sectional view and a top view, respectively, of a prior art interconnect structure 12 having a suspended portion 14 over a silicon substrate 10. Interconnect structure 12 includes an inner conductor 20, an insulating dielectric coating 18 and an outer conductive layer that serves to encapsulate the insulating dielectric coating 18. Interconnect structure 12 also includes two contact posts 13 fabricated that have a larger dimension so as to support suspended portion 14.
It should be noted that the suspended portion 14 tends to sag under the influence of gravity. Therefore, there is a limit to the length of such structures before they fracture and break, which is a significant practical problem in implementing this prior art structure. Another problem encountered with the interconnect structure of FIG. 1A is the inability to stack multiple interconnect layers. By way of example, if a second interconnect structure were built over structure 12, the probability of breaking center region 14 dramatically increases due to the lack of mechanical support under center region 14. For a more detailed description of the steps associated with fabricating this prior art interconnect structure, reference may be made to a paper entitled xe2x80x9cVLSI Multilevel Micro-Coaxial Interconnects for High Speed Devicesxe2x80x9d by M. E. Thomas, et al., Fairchild Research Center, National Semiconductor Corporation, Santa Clara, Calif., IEDM Tech. Dig., pages 55-58 (1990), which is hereby incorporated by reference.
Another drawback of integrating RF circuitry into chips that are primarily designed for digital CMOS circuits is co-axial lines 12 must be integrated at the top-most metallization level of a chip. This presents significant limitations in the number of RF lines that can be used to complete RF signal processing for a given chip. Therefore, designers wanting to integrate RF lines over predominately CMOS chips must design the chip substantially larger to enable the desired number of RF lines to appropriately be integrated to the top metal layer of the chip. This limitation is well known to circuit designers, and therefore, it is often determined to be more advantageous to use separate chips for CMOS circuitry and RF circuitry.
As shown in FIG. 1C, designers of cellular phones typically find it more practical to use a CMOS chip 52 for performing digital signal processing and a separate RF circuit 55 to process RF signals. This is commonly preferred due to the limitations of trying to integrate RF lines onto chips that are custom fabricated for CMOS digital processing. Nonetheless, an arrangement of this sort presents problems, among them fabrication costs, power losses, signal losses and additional packaging complexities. Circuit 50 requires that RF circuit 55 and the CMOS chip 52 be individually fabricated and integrated onto the printed circuit board (PCB) 51. This increases manufacturing costs and manufacturing time.
Microwave and RF applications operate at high frequencies. The high frequencies require the use of co-axial lines or waveguides. When these lines are integrated with standard CMOS lines, a large loss of power occurs. In order to compensate for these losses, amplification circuitry may be necessary.
As signals are communicated back and forth from RF circuit 55 and CMOS chip 52, signal loss will naturally occur. Henceforth, this signal loss reduces overall efficiency of a circuit implementation needing both digital CMOS and RF circuitry. In order to overcome these losses, signal conditioning may be necessary to improve signal integrity. However, the use of such devices will aggravate the problem of packaging that already exists with the prior art.
Packaging inefficiencies of the prior art circuit using RF circuit 55 and CMOS chip 52 make this type of circuit undesirable. In order to integrate separate RF circuit 55 along with CMOS chip 52, greater amounts of space on the PCB will be required, thereby forcing portable electronics (e.g., cellular phones) to be packaged in larger housings.
In view of the foregoing, there is a need for a circuit which integrates an RF circuit with a CMOS chip which avoids the problems of the prior art. This new circuit should be easy to manufacture, maintain power and signal strength, avoid the use of prior art co-axial lines and come in a more space efficient package. Additionally, this circuit should be able to handle high speed applications, including RF and microwave applications.
Broadly speaking, the present invention fills these needs by providing an integrated circuit device which can integrate both standard CMOS circuitry and co-axial lines that are capable of handling RF signals, microwave signals and other high speed signals, and methods for making such a device. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a method of forming a co-axial interconnect line in a dielectric layer is disclosed. The method includes defining a trench in the dielectric layer and then forming a shield metallization layer within the trench. After forming the shield metallization layer, a conformal oxide layer is deposited within the shield metallization layer. A center conductor is then formed within the conformal oxide layer. Once the center conductor is formed, a fill oxide layer is deposited over the center conductor. A cap metallization layer is then formed over the fill oxide layer and is in contact with the shield metallization layer.
In another embodiment, a semiconductor device incorporating a co-axial interconnect line is disclosed. The semiconductor device includes a dielectric layer and a trench defined within the dielectric layer. A shield metallization layer is defined over the dielectric layer and along the trench. The semiconductor device also includes a center conductor contained within the shield metallization layer. An oxide layer surrounds the center conductor. In addition, a cap metallization layer is defined over the oxide layer and over the shield metallization layer, such that the cap metallization layer is in electrical contact with the shield metallization layer. The cap metallization layer and the shield metallization layer form an outer shield of a co-axial line and the center conductor forms the inner conductor of the co-axial line.
In yet another embodiment, a method for making a semiconductor device with co-axial interconnect lines in a CMOS chip for high speed applications is disclosed. The method includes forming a trench in a base dielectric layer and forming a shield metallization layer over the base dielectric layer and the trench. After the shield metallization layer is formed, a conformal oxide layer is deposited over the shield metallization layer such that the conformal oxide layer defines a region within the trench. Once the conformal oxide layer is deposited, a liner metallization layer is formed over the conformal oxide layer and over the region within the trench. Next, a conductive layer is disposed within the liner metallization layer to fill the region within the trench with conductive material. After the conductive layer is disposed within the liner metallization layer, the conductive layer is etched along with the liner layer to define an inner conductor within the region that is defined within the trench. Next, an oxide layer is formed over the inner conductor that is defined by the liner layer and the conductive layer, whereby the oxide layer is configured to fill the region within the trench. The oxide layer and the conformal oxide layer are then planarized down to the shield metallization layer. A cap metallization layer is then formed over the shield metallization layer, the conformal oxide layer, and the oxide layer defined within the trench.
The many advantages of the present invention should be recognized. A semiconductor application can now integrate co-axial features and standard CMOS features on a single chip, and the co-axial features can be integrated on any level of a chip""s interconnect region. As such, designers are no longer required to design and fabricate separate chips having co-axial lines and CMOS chips to make a desired integrated circuit application.
As a further advantage, there is no power and signal losses due to separate chip integration, increased fabrication time and costs, and the need for larger silicon area to design simple or complex circuits. Also, the present invention has the ability to handle high speed applications, such as RF, microwave applications and other applications operating at frequencies up to and greater than 1 GHz. Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.